The proposed research focuses on understanding how Generalized Anxiety Disorder (GAD) may be experienced differently in older adults compared to middle-aged adults. Though little research has been conducted on GAD in older adults, anxiety symptoms, in general, are as common as depressive symptoms in this age group. GAD is one of the most common anxiety disorders, and is associated with increased health care usage and poorer quality of life. Developmental changes related to aging, such as physiological changes in autonomic arousal, memory changes, and increased prevalence of disease, could lead to differences in how GAD is manifested. A series of three studies is proposed that investigate three broad areas related to GAD: 1) differences in GAD-related symptom reporting by older adults compared to middle-aged adults; 2) the relationship of personality characteristics to lifetime GAD; and 3) genetic and environmental influences on the lifetime GAD All studies use a population-based sample of data drawn from the Screening Across the Lifetime Twin study based on the Swedish Twin Registry. The main outcome variable is lifetime GAD derived from a telephone screening procedure using the Computerized International Diagnostic Interview-Short Form. Rasch modeling techniques will be used to assess whether different cohorts report different combinations of GAD-related symptoms, despite having similar overall level of symptoms. The impact of personality traits on lifetime GAD will be assessed using non-parametric multiple discriminant analysis. Finally, to assess the role of genetic and environmental factors on lifetime GAD, behavior genetic models will be tested.